Blackboard-eraser



('No Model.) 4 l v f- 1S'. C. DAVIS BLAGKBOARD lRASER.`

l\Io.L102,5'70. Patented May '7, 1889.

Humm l .A MMM' 1r; A A

A A UNITED. STATES PATENT OFFICE.

STILLMAN C. DAVIS, CAMBRIDGE, MASSACHUSETTS.

BLAc'KBoARD-ERASER.

SPECIFICATION forming part of Letters Patent No. 402,570, dated May 7, 1889.

Application filed May 5, 1888. Serial No. 272,972. (No model.)

boards employed in all educational institutions, and to all other uses and purposes to which my invention before mentioned may be applicable, and is an improvement upon the invention described in Letters Patent of the United States of America, numbered 254,094, issued to John F. Freese and myself as assignees of Chauncey M. Lothrop, dated February 2l, 1882.

VIt consists of a new and improved method of securing and retaining the fabric or material used for erasive purposes when inserted in the hand block or frame. It simplifies the manner and labor of making renewals of the eraser when such renewals are necessary. It enables me to make use of certain articles of great economy and utility for crasive purposes which it was found impracticable to use before.

In order to a full understanding of the utility, extent, and merit of my invention, for which application is hereby made for Letters Patent, reference is made to the accompanying drawings.

Figure l is a longitudinal vertical throughsection of the hand blocker frame. Fig. 2 shows the plan of the perforated metal plate herein described. Fig. 3 shows a longitudinal vertical section of the perforated metal plate. Fig. 4. shows the manner of applying the perforated metal plate to the pieces of crasive material.

Aindicates the frame or body of the eraser, preferably constructed from wood, and in form rectangular, of sufficient thickness to insure strength and durability. The lower or under part of the bodyAis scarfed away onehalf its length, (or, if preferable, the additional thickness may be obtained by the addition of material united to the part A on the dotted line 19,) to admit the attached and duplicated body B, which is 'secured to the upper body, A, at the point C by leather or other cheap and durable material. At each end of the framesAand B are mortised openings or grooves D D, extending the width of the body.

My invention, forwhich I make application for Letters Patent, consists in applying to the ends of the pieces of fabric, or whatever material it :may be desirable to use for crasive purposes, a narrow strip or band of ordinary tin, Zinc, iron, or other metal plate, perforated (or, as it is known to the trade, stabbed in the manner shown in Fig.. 2. I adopta method of perforation that produces on the under side of the metal platea sharp projecting burr similar to the burrs on the tin graters used for household purposes. The strips may be of any desired width, preferably from three-eighths to three-fourths of an inch Wide. These strips of perforated metal plate, with the burrs next to the material, are folded or bent around the ends of it, and by subjecting them to a heavy pressure the burrs are forced down into the fabric or other material, securing it firmly and rigidly, in the manner shown in Fig. 1l. When thus treated, the

pieces of crasive material can be easily and quickly inserted in the grooves D D of the hand block or frame. It greatly facilitates the labor of removing and cleaning the same. It obviates the liability heretofore existing to become loosened and displaced when in use. The labor of making renewals 'of the crasive material is greatly simplified` and reduced.

The rigid metal bands serve to support andof au adjustable eraser-strip with pieces of perforated ,metal plate rigidly attached to thel ends, all substantially as set forth.

In testimony whereof I have signed my name to this specification, in the presence of two sub- Io soribng Witnesses, on Athis 30th day 0f April,

2. In a blackboard-eraser, the combination A. D. 1888. of a hand block or frame with an adjustable STILLMAN C. DAVISl eraser-strip having attached to eaoh end there- Witnesses: v

of strips of metal plate perforated in the mauner shown, as and for the purpose speoiied.

WALTER E. LOMBARD, FRANK E. BRAY. 

